DE2842114C2 - Binder for CO 2 curable molds - Google Patents

Description

(A) 100 parts by weight of at least one alkali-neutralized carboxy group-containing polymer, which is selected from ar-olefin-maleic anhydride copolymers, Styrene-malelic anhydride copolymers and methyl vinyl ether-maleic anhydride copolymers,

(B) 100 to 300 parts by weight of an oxide and / or hydroxide of a polyvalent metal

and

(C) a water-soluble organic compound,

characterized in that it is 3 to 40 parts by weight of a water-soluble organic compound (C) contains polyhydric alcohol.

3. molding binder according to claim 1 or 2, characterized by a carboxyl group Copolymer (A) with ethylene, propylene, n-butene, isobutene, n-pentene, isoprene or 2-methyl-1-butene as the ar-olefin component.

4. Molding binder according to one of claims 1 to 3, characterized by slaked lime as Polyvalent metal hydroxide (B).

5. Molding binder according to one of claims 1 to 4, characterized by slaked lime and Zinc hydroxide as hydroxides of polyvalent metals (B).

6. Molding binder according to one of claims 1 to 5, characterized by ethylene glycol, diethylene glycol. Glycerin. Propylene glycol. Sorbitol, mannitol or 3-methylpcntane-1.3.5-trol as polyvalent ones Alcohol (C).

The invention relates to binders for with gaseous CO; Hürlbaren casting molds according to the generic term of claims 1 and 2.

In conventionally used molds for metal casting, inorganic binders such as Sodium silicate and phenolic resins. Furan resins and other organic binders used. Such .'irnen can with the pressure and the heat Resist casting of the molten metal, however, the molds have an inorganic binder after casting only a low disintegrability, which is why the demolding step for removing the Casting is difficult, which in turn increases the number of process steps for making castings is increased. Such problems do not arise in the case of casting molds using organic binders.

As a method for hardening casting molds, there are currently a self-hardening method by chemical means Reaction of the binder components added to the molding sand as well as a cold hardening process for hardening of casting molds by introducing COj gas or gaseous amines into the mold after it has been introduced of the molding sand containing the binder is available around the model.

In the former process for mold hardening, a chemical reaction begins at the same time as the Addition of the binder to the molding sand, which makes the processing of the molding sand suitable for the application available processing time is limited.

The last-mentioned procedure includes the so-called COi method for hardening by blowing gaseous COj into the molding sand containing sodium silicate as a binder, a method for hardening by blowing a gaseous amine into a hydroxyl-containing resin such as a phenolic resin and a polyisocyanate as a binder-containing molding sand, and a process for hardening molding sand, which contains a combination of a copolymer of an acrylic acid ester with ammonium acrylate and sodium acrylate or a phenolic resin with calcium hydroxide, with gaseous CO ₂ .

Such molding sands can have a longer processing time than with a chemical reaction of the binding agent components can be achieved in the molding sand, the mold being hardened immediately by introducing the gas can achieve higher productivity.

However, since _{sodium sulfate is used as a binder in the CO 2} process, molds produced in this way cannot be dismantled; the processes in which gaseous amines are used also pose problems with regard to the toxicity of the substances used and the odor of the amines.

The process based on the combined use of copolymers of acrylic acid esters and ammonium acrylate as well as sodium acrylate and calcium hydroxide with gaseous COi brings with it the following problems: (1) During the production of the molding sand or during molding, ammonia gas is released, which leads to environmental pollution and raises occupational health problems; (2) Immediately after the CO ₂ gas is blown, sufficient strength cannot be obtained.

Those processes in which phenolic resins are used do not lead to environmental pollution or to occupational hygiene problems due to the release of ammonia gas and the like, however the hardening of the mold after the introduction of the gas takes place only by drying, whereby the strength the shape is increased less.

Furthermore, there is known a method of making molds which is based on the combined use of Polyvinyl alcohol and calcium hydroxide or calcium oxide and COj gas based; with this procedure solve the problems of the COj method and others conventional prior art mold making processes and a considerable amount technical progress compared to previous ones

Achieve procedures, however, difficulties arise with this procedure with regard to a Uniform curing of the inside of the mold when large-sized molds are produced.

The older patent application P 28 14 357.9, which is _{perceived as state of the art, shows CO 2} -hardening binders that contain the following components:

(A) 100 parts by weight of at least one alkali-neutralized carboxyl group-containing polymer,

which is selected from or-olefin-maleic anhydride copolymers, Styrene-maleic anhydride copolymers and methyl vinyl ether-maleic anhydride copolymers.

(B) 100 to 300 parts by weight of an oxide and / or hydroxide of a polyvalent metal

and

(C) a water-soluble organic compound.

20th

The invention is based on the object of specifying a molded part in which the above-mentioned problems do not occur, but the advantages of conventional binders are achieved; the molding binder should have the following properties: (1) easy production of the molding sand; (2) easy removal of the binding agent by washing with water, even if the body or clothing is contaminated with the binding agent! have been polluted; (3) longer processing time of the molding sands; (4) higher dimensional stability; (5) Improvement in occupational hygiene by improving the air at the workplace in the manufacture of molds; (6) Improving productivity in molding and (7) achieving the desired dimensional stability using lower CO ₂ gas fans

The object is achieved according to the characterizing part of claims 1 and 2, respectively. Advantageous further training are the subject of the subclaims.

The binder according to the invention has the advantages of the CO ₂ process and the advantageous properties of binders in which organic binder components are used at the same time.

Polymers with carboxyl groups used according to the invention (A) are styrene-maleic anhydride copolymers, Methyl vinyl ether-maleic anhydride copolymers and α-olefin-maleic anhydride copolymers. For those carboxyl-containing polymers which are easily soluble in water, water can be used as a solvent without addition; for in water Polymers which are poorly soluble or insoluble are aqueous alkali metal hydroxide solutions used as solvents.

The oxides or hydroxides of polyvalent metals which can be used according to the invention include oxides or Hydroxides of calcium, magnesium, barium, zinc. Aluminum, iron and the like, also include also those substances which contain these oxides or hydroxides as constituents, for example Bentonite, clays, talc or satin white as well as the aluminum sulfate-calcium hydroxide complex x.

Among the substances mentioned above are the oxides and hydroxides of calcium, magnesium and barium particularly preferred. Of the above metal oxides or hydroxides can only be selected from the calcium group one connection is used in each case; with regard to the other oxides or hydroxides is the same Use of two or more compounds, possibly using a compound of the calcium group, cheaper.

The metal oxides or metal hydroxides (B) are used in an amount of 100 to 300 parts by weight per 100 Parts by weight of the carboxyl-containing polymer (A) are used.

The metal oxides or hydroxides used as components for the binder according to the invention can either be previously suspended in an aqueous solution of the polymer or the molding sand alone can be added.

The sodium salt of gluconic acid used according to the _{invention has the formula C 6 Hii07Na.} The sodium gluconate is used in an amount of 3 to 50% by weight, based on the weight of the carboxyl-containing polymers in the aqueous solution.

The polyhydric alcohol increases strength in the initial stage of molding; it can be the binder composition either added beforehand or added to the molding sand alone. The multi-valued one According to the invention, alcohol is used in an amount of 3 to 40% by weight, based on the weight of the carboxyl-containing Polymers in the aqueous solution added.

The polyhydric alcohols which can be used according to the invention include, for example, ethylene glycol, glycerol, Propylene glycol, sorbitol, mannitol and other polyhydric alcohols and their derivatives.

To dissolve the carboxyl group-containing Polymers (A) in water is the use of an alkali hydroxide or water glass or the like required, whereby alkali metals such as Na, K, etc. are bound to the carboxyl groups of these polymers, which thereby become water-soluble.

The styrene-maleic anhydride copolymers used according to the invention, Methyl vinyl ether-maleic anhydride copolymers and ar-oletin-malelic anhydride copolymers can also include terpolymers; in the case of the sr-olefin-maleic anhydride copolymers can accordingly not only copolymers of 7-olefin and maleic anhydride, but also Terpolymers of, for example, ^ -olefin, maleic anhydride and maleic acid diesters are used. To the copolymers of x-olefin and maleic acid monoesters also include not only the copolymers of ar-olefin and maleic acid monoesters themselves, but also copolymers of these two components as essential components with another component, for example terpolymers of z-olefin. a maleic acid monoester and a maleic acid diester and the same.

The jr-olefins used according to the invention are straight-chain or branched olefins with 2 to 8 and preferably 2 to 6 carbon atoms, for example ethylene. Propylene, η-butene, isobutene, n-pentene, isoprene. 2-methyl-1-butene and the same.

The binder according to the invention can also be used to increase the binding force, the water resistance or to Adjustment of the viscosity depending on the added amounts of components (A) to (C) with sawdust or wood pulp, various emulsions. I.alices and the like are mixed.

The molding material according to the invention can be packaged in the following three ways (I), (II) and (III):

(D First partial pack: neutralized with alkali aqueous solution of the carboxyl-containing polymers (A); second partial pack: metal oxide or hydroxide (B) and third part pack: Sodium gluconate (C):

(II) First partial pack: suspension of the metal oxide or hydroxide (B) in a neutralized with alkali

aqueous solution of the carboxyl-containing polymers (A) and second subpack: sodium gluconate (C);

(III) Complete package: Mixture of the in one with Alkali-neutralized aqueous solution of the carboxyl-containing polymers (A) suspended metal oxide or hydroxide (B) further mixed with sodium gluconate (C).

The molding binders according to the invention can also be used in the following three pack types (IV), (V) and (VI) are present:

(IV) First part pack: aqueous solution of the carboxyl group-containing polymers neutralized with alkali (A); second part pack. Metal oxide or hydroxide (B) and third subpack: polyvalent alcohol (C);

(V) First partial pack: suspension of the metal oxide or hydroxide (B) in a neutralized with alkali aqueous solution of the carboxyl-containing polymers (A) and second subpack: more little alcohol (C);

(VI) Complete package: mixture of the carboxyl group-containing in an aqueous solution neutralized with alkali Polymer (A) suspended metal oxide or hydroxide (B) in a further mixture with the polyhydric alcohol (C).

By adding the respective packs to the molding sand, corresponding molding sands with binding agents can be added getting produced.

The molding sands obtained in this way are poured in around the model; then it is put in with the molding sand Filled mold COi gas introduced, which immediately hardens the mold. The resulting shape is as Suitable for casting.

If, on the other hand, the molding sands are _{kept gas-tight without any supply of CO 2} gas, the molding sand does not harden and can accordingly be stored for a long time.

When the binder according to the invention is used, the above can be used as a basis Achieve the stated advantages.

The invention is explained in more detail below with reference to exemplary embodiments, their details are not limiting.

example 1

120 g of isobutene-maleic anhydride copolymer (Molar ratio 1:!) And 50g NaOH were mixed with 180g Water mixed and brought into solution by heating to 90 ° C. The resulting solution was made with 300 g of slaked lime and then 500 g of 5 »water are added to form a white suspension to thin. The resulting suspension was mixed with 360 g of a styrene-Buiadlen copolymer latex (SBR latex) (Solids content 50% by weight) and 10 g of sodium gluconate mixed (binder 1).

40 g of this binder were mixed with 1 kg of quartz sand JIS No. 100 (maximum of the grain size distribution function with a grain size of 0.147 mm (100 mesh)]: test specimens 50 mm in diameter and 50 mm in length were produced from the mixture obtained by ramming s were treated with COj gas under a pressure of 1 kg / cm ² .

The increase in strength as a function of the time after production of the test specimens was investigated: the results obtained are listed in Table 1 (> = ■ ).

Tabel

Compressive Strength (Kg / cm ² )

Time after
Forming (h)

Test specimen with
Binder 1

right away
thereafter

7.5

1 2 3 5 24

12 14 18 23 40

As can be seen from Table 1, the strength immediately after molding was the increase in strength with time as well as the strength after 24 h high, at the same time there were good industrial hygiene conditions since no air pollution occurred.

Example 2

120 g of styrene-maleic anhydride copolymer and 50 g of NaOH were mixed with 180 g of water and dish by heating in solution. The resulting solution was then quenched with JÖl'g Ka! K, 500 g of water and 5 g of sodium gluconate are added and the mixture is stirred to form a white suspension (binder 2).

120 g of methyl vinyl ether-maleic anhydride copolymers and 50 g of NaOH were mixed with 180 g of water and brought into solution by heating. The resulting solution was then washed with 300 g of slaked lime. 500 g water and 5 g sodium gluconate added and stirred into a white suspension (binder 3).

The strength test of test specimens produced using binders 2 and 3 was carried out with the same mixing ratio and the same COj gas treatment as in Example 1. The results obtained are shown in Table 2.

Table 2

Compressive strength (kg / cm ^:)

Time after
Molding

Binder 2
Binder 3

immidiatly after

6.1
6.3

24

25 30

Example 3

25 g of isobutene-maleic anhydride copolymer and 13 g of NaOH were mixed with 62 g of water and mixed brought into solution by heating to 65 ° C. The resulting solution was then added with 60 g Slaked lime, 1.25 g zinc hydroxide, 20 g SBR latex, 50 g water and 5 g sodium gluconai mixed and added mixed with a white binding agent suspension (binding agent 3).

The compressive strength of test specimens produced therefrom in the same mixing ratio as in Example 1 was 7.4 kg / cm ^J immediately after molding and 34 kg / cm ² after 24 h.

Example 4

The isobutene-maleic anhydride copolymer, NaOH and water prepared according to Example 3

Solution was not created immediately after the solution was made, but rather when the molding sand was made with the corresponding amounts of the other additives from Example 3 and also separately with 10 g slaked lime and 3 g sodium gluconate mixed, whereupon the same tests as In Example I were carried out on test specimens produced therefrom.

The compressive strength was found to be 6.2 kg / cm ² immediately after molding and 34 kg / cm ² after 24 hours.

Example 5

A molding sand mixture was prepared from the binder 1 of Example 1 as in Example I, using quartz sand JIS No. 65; a mold was produced from this, the hardening properties of which were investigated. The binder had reactivity to COj and a high hardening rate, which enabled high productivity in the manufacture of molds. The mold could also be hardened with only small amounts of CO ₂ , which allowed very economical mold production. After curing, the mold was completely and evenly cured to a layer length of 300 mm.

Example 6

From the binder 1 of Example 1 was as In jo Example 1 produced a molding sand mixture from which a casting mold was produced. Inside was an engine case poured from a weight of 18 kg.

The investigation showed that there were no casting defects and that the shape, particularly in the core part, was good Can be dismantled.

Example 7

A binder was prepared as in Example 1 with the difference that instead of sodium gluconate 10 g of glycerol were used (binder 4); as in Example 1, test specimens were produced therefrom and examined.

The results obtained are shown in Table 3.

Table 3

Compressive strength (kg / cm-)

Time after
Forming (h)

Test specimen with
Binder 4

right away
thereafter

7.8

1 2 3 5 24

13 16 18 23 40

As can be seen from Table 3, the strength immediately after molding was the increase in strength with time and the strength after 24 hours was high, and the occupational hygiene conditions were very good good because no toxic or unpleasant gases or vapors were produced.

Example 8

120 g of styrene-maleic anhydride copolymer and 50 g of NaOH were mixed with 180 g of water and brought into solution by heating. The resulting

40

45

50

50

65 solution was then with 300g slaked lime. 500 g of water and 5 g of sorbitol were added, after which the mixture was stirred to form a white suspension (binder 5).

120 g methyl vinyl ether maleic anhydride copolymer and 50 g of NaOH were mixed with 180 g of water and brought into solution by heating. The resulting solution was then added with 300 g Slaked lime, 500 g of water and 5 g of diethylene glycol mixed, after which a white suspension (binder 6) was stirred.

The strength test with the binders 5 and 6 test specimens produced were carried out using the same mixing ratio and the COj gas treatment as in example I.

The results obtained are shown in Table 4.

Table 4 Dfuikicsügkcii ikg / cm-'i right away 24 Time after thereafter Molding 6.1 25th Binder 5 6.3 30th Binder 6 Example 9

A binder was prepared as in Example 3 with the difference that instead of sodium gluconate 5 g of ethylene glycol were used; As in Example 1, test specimens were made from this material (binder 7) manufactured and examined.

The compressive strength was found to be 7.4 kg / cm ² immediately after molding and 34 kg / cm ² after 24 hours.

Example 10

The isobutene-maleic anhydride copolymer. NaOH and water solution prepared in Example 9 was not immediately after the solution was made, but only when the molding sand was made with the corresponding amounts of the other additives of Example 3 added, furthermore 10 g slaked lime and 3 g of 3-methylpentane-1.3.5-triol were added (binder 8); the specimens were produced and tested as in Example 1.

The compressive strength was found to be 7.8 kg / cm ² immediately after molding and 39 kg / cm ² after 24 hours.

Example 11

As in Example 1, a molding sand mixture was produced from the binder 4 from Example 7. From it a mold was made, the hardening properties of which were examined. The shape was according to the Hardening to a layer length of 300 mm, completely and evenly hardened.

Example 12

As in Example 1, a molding sand mixture was produced from the binder 4 from Example 7. From it a mold was made in which a motor housing weighing 18 kg was cast.

The examination showed that there was no casting defect, and the shape. Particularly in the core part, it was easy to dismantle.

It follows from the experimental results that the binder according to the invention has good reactivity with COj and has a high curing speed, which is why Gudforms are made with high productivity have made; the molds can also be cured with only a small amount of COj, what the profitability of the mold making increases.

Claims (2)

Patent claims: 1. Binder for casting molds curable _{with gaseous CO 2 based on} (A) 100 parts by weight of at least one alkali-neutralized carboxyl group-containing polymer, which is selected from or-olefin-malelic anhydride copolymers, Styrene-maleic anhydride copolymers and methyl vinyl ether-maleic anhydride copolymers, (B) 100 to 300 parts by weight of an oxide and / or hydroxide of a polyvalent metal and (C) a water-soluble organic compound, characterized in that it is 3 to 50 parts by weight as the water-soluble organic compound (C) Contains sodium gluconate. 2. Binder for gaseous COi curable Molds based on